Thanks for your questions! Shouts are typically made up of three rotmulaag, or "Words of Power". There are no requirements for what part of speech a Word of Power has to be. For example, one Shout might be all nouns (Raan Mir Tah 'Animal Allegiance Pack') while another Shout might be all verbs (Krii Lun Aus 'Kill Leech Suffer').

You can see a full list of Shouts and Words of Power here.

When discussing lore and how things work, it's important to separate lore from game mechanics. As an obvious example, the Dragonborn isn't physically capable of freezing time and downing dozens of wheels of cheese. The item menu is a game mechanic. Similarly, Thu'um cooldown is a game mechanic. Dragons in Elder Scrolls lore aren't limited to Shouting in 30-second intervals. Even the three-word Shout structure is a game mechanic. In lore terms, any number of words could produce a Thu'um.

To get the ability to Shout in Skyrim, you'll want to follow the Main Quest. After escaping Helgen, speak to Jarl Balgruuf in Whiterun. Eventually you'll be sent into an Ancient Nord ruin where you'll learn your first Word of Power, and later encounter the means to unlock it.

Adding to paarthurnax's answer: while there are no explicit limitations for what parts of speech are allowed, known Shouts tend to consist of verbs and/or nouns. Their glosses do not typically form grammatical sentences. The only exception is the four-word sil los dii du "souls are mine to devour" spoken by Miraak.